Method for looping a coating structure around a bead core in motor-vehicle tires

ABSTRACT

A method and apparatus for applying a ribbon-like coating structure to the outer surface of a tire bead core. A bead core (2) is coaxially placed around a support drum (6) carrying an inflatable air bag (7) disposed in a deflated condition. Clasping sectors (14) circumferentially distributed in the drum are radially moved close to the inner surface of the bead core (2) to make a central portion of a ribbon-like coating structure (3) arranged about the inflatable air bag (7), adhere against the bead core itself. The air bag is inflated so as to form, on opposite axial sides relative to the bead core (2), two lobes (17, 18) each of them being enclosed between the outer surface of the drum (6) and a respective annular opposition bell (19, 20) coaxially encircling the drum. By axially moving the opposition bells (19, 20), a first and a second side flap of the coating structure (3) are applied to respective surfaces of the bead core (2). The second flap overlaps the first flap and is fastened thereto on the radially external surface of the bead core (2).

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for looping acoating structure on bead cores in motor-vehicle tires.

It is known that incorporated in vehicle tires, at the so-called "beads"defined along the inner peripheral edges of the tire, are respectiveannular metal elements, circumferentially inextensible, currentlyreferred to as "bead cores"; said bead cores perform a dual function,that of suitably stiffening the beads themselves for ensuring theirstable connection with the rim on which the tire is mounted, and that ofproviding a steady anchoring to the carcass plies usually arranged inthe tire itself.

In a particular embodiment, especially used with tubeless tires forheavy duty motor transport, said bead cores are formed with a pluralityof bare metal wire coils having a right polygonal, preferably hexagonalsection, disposed axially and radially close to each other so as toconstitute an annular element having its radially inner surface inclinedat 15° relative to its own axis: a plurality of clips, usually made of ametal material, distributed along the peripheral extension of saidelement and closed at the right section of same, keeps the elementcompact and its sectional shape constant during the tire manufacturingprocess.

The foregoing being stated, it is to be pointed out that during the tiremanufacturing process suitable expedients are to be adopted so that aperfect adhesion of the bead core to the other elastomer components ofthe tire is ensured. The presence of detachment areas and air bubblesentrapped between the bead core and elastomer material disposed aroundsaid bead core would be in fact very detrimental to the structureintegrity of the tire in use.

To this end, a coating structure made of elastomer material is providedto be applied to the bead core, which coating is adapted to be steadilyanchored to the bare metal wires forming the bead core itself and toprovide an appropriate attachment surface for the elastomer materialcomponents to be further assembled therewith.

To this end, of the great number of known structures, the structuredescribed in U.S. Pat. No. 5,261,979 issued Nov. 16, 1993 in the name ofthe present assignee has proved to be of particular interest. Itconsists of a layer of elastomeric material directly wrapped on the beadcore itself and a rubberized fabric ribbon provided with reinforcementcords of heat-shrinkable material wrapped around the elastomericmaterial layer so that said cords are disposed in a direction transverseto the longitudinal extension of the bead core.

In fact, during the tire vulcanization step, an excellent bonding isachieved between the elastomeric material and the bead core, due to thefavorable compression action produced on the layer material as a resultof the shrinkage of the rubberized fabric cords.

According to the above teachings, the coating structure that can beconveniently prepared separately by assembling the elastomeric materiallayer and rubberized fabric ribbon, so as to form a strip of appropriatewidth cut to size, is preferably enfolded loop-wise around the beadcore, so that it integrally embraces the cross sectional profile of thebead core itself and locked in said position by overlapping of thelongitudinal edges thereof.

This process is particularly convenient when bead cores of the describedtype are involved, in that it easily overcomes the difficulty embodiedby the presence of clips along the peripheral extension of the beadcore, which clips give rise to the discontinuity of the surface to becoated making it difficult to use other known methods and machines thatbring about a serious negative impact on the final result of theoperation.

Unfortunately this looping operation which is easy to do when bead coresof rubberized metal wire are involved, has proved to be a source ofseveral drawbacks, both during its execution and as regards the qualityof the finished product, when put into practice according to the knownart with bead cores of the pack type, made of bare metal wires aspreviously described.

This is due to the fact that, with these bead cores, the stablepositioning of the ribbon-like structures enfolded on the bead coreexclusively depends on the mutual adhesion between the side edges of thecoating structure itself, suitably overlapped and pressed against eachother by said enfolding operation.

In fact, the adhesion of the raw elastomer material on the bare metal(that is not rubberized) is rather weak and at all events insufficientto ensure the temporary attachment of the first side flap of the coatingstructure to the bead core during the enfolding or looping operation,above all in the case in which said structure comprises nylon fibers orthe like tending to resiliently take on their original conformationagain after their enfolding about the bead core section.

In this case, due to the weak adhesiveness between the metal forming thebead core and the elastomeric material forming the coating, the elasticshrinkage of the material can cause separations and slidings of thefirst flap on the bead core, before said first flap is sealed to thesecond flap: the result is a loop which is not tensioned and canincorporate air bubbles and where the overlapping width between the twoflaps varies along the longitudinal extension of the bead core, whichrather often also gives rise to openings proper at the junction pointbetween the two flaps, thereby making the shrinkage action developed bythe cords during the tire vulcanization inefficient.

The problem does not seem to be resolvable with the teachings of U.S.Pat. No. 4,450,025, according to which the two flaps are first sealed toeach other, at their surfaces axially internal to the loop and disposedin a diametrical plane of the bead core, then the sealed portion of thecoating is folded back against the bead core surface.

A drawback present in this solution is, among other things, the factthat the overlapped flaps exhibit an unacceptable thickness at thejunction, as compared to the quality standards presently required fromthe tires.

SUMMARY OF THE INVENTION

According to the present invention it has been found that by carryingout looping by means of an inflatable air bag defining, on laterallyopposite sides of the bead core being worked, two lobes enclosed withinrespective annular opposition bells, axially movable and independent ofeach other, it is possible to keep the first side flap of the coatingstructure applied to the bead core while the second flap is being laiddown, as far as overlapping between the two flaps begins, therebyeliminating the risk that an important portion of the first flap may bedetached from the bead core before the second flap is applied theretoand therefore overlapping of the two flaps has occurred.

In a first aspect, the invention relates to a method for looping acoating structure on a motor-vehicle tire bead core, characterized inthat it comprises the steps of:

circumferentially laying down a ribbon-like coating structure comprisingat least one raw elastomeric material layer on a median region of aninflatable air bag flattened against an outer cylindrical surface of asupport drum;

placing a bead core being worked to a coaxial position with, and closeto said coating structure circumferentially laid down on the inflatableair bag, said coating structure having an overall width slightly greaterthan the circumference of the cross-sectional bead core profile;

pressing a plurality of clasping sectors circumferentially distributedon the support drum against the radially inner surface of the bead core,in order to fix the mutual positioning of the bead core and coatingstructure on the inflatable air bag;

inflating said air bag causing the radial expansion thereof in order tolaterally bend, on opposite sides with respect to the bead core and uponthe action of a first and a second lobe defined by the air bag itself, afirst and a second side flap of the coating strip towards a first and asecond side surface of said bead core;

counteracting the radial expansion of said lobes by a first and a secondannular opposition bells each of them being disposed in coaxial relationaround one of said lobes;

axially moving the first annular opposition bell towards said bead core,enfolding around it the first lobe of said air bag for progressivelyapplying the first side flap of the coating structure to thecorresponding side surface and at least one portion of the radiallyouter surface of the bead core;

axially moving the second annular opposition hell towards said beadcore, enfolding around it the second lobe of said air bag forprogressively applying the second side flap of the coating structure tothe corresponding side surface and the uncoated (that is not coated withsaid first flap) surface portion of the bead core;

axially drawing the first annular bell away from the bead core whilekeeping on with the axial displacement of the second opposition bell fordisengaging said first lobe from the first side flap of the coatingstructure immediately before the end edge of said second side flap isapplied to the radially outer surface of the bead core coated with saidfirst flap, so that said first and second side flaps are mutuallyfastened along the respective end edges overlapping each other at theradially outer surface of the bead core.

Preferably, the circumferential laying down of said coating structurecomprises the steps of: circumferentially depositing at least one ribbonof rubberized fabric reinforced with heat-shrinkable material cords onsaid inflatable air bag; circumferentially depositing a layer of rawelastomeric material around said ribbon.

Advantageously, the radial extension of the air bag is stabilized to apredetermined and constant value, on varying of the inflating pressureof the air bag itself. The air bag is made axially inextensible and thuswhen counteracting the radial expansion of the inflatable air bag,adjustment of the axial expansion (and, of course, appropriate controlof the expansion profile of each lobe), at the same time also becomespossible.

In a specific embodiment of the invention, said air bag is inflated to apressure of between 2 and 4 bars, identical in both lobes, in that afluid communication between the first and second lobes of the inflatableair bag is constantly maintained.

In a second aspect, the invention relates to an apparatus capable oflooping up a coating structure on a motor-vehicle tire bead core,characterized in that it comprises:

a support drum;

an inflatable air bag having two circumferential anchoring beadscoaxially fastened to the support drum, two connecting portionsextending mutually away from said anchoring beads and one work portionradially external to said drum and extending between opposite ends ofsaid connecting portions;

a plurality of clasping sectors distributed circumferentially around thedrum and radially movable relative thereto between a rest position inwhich they are radially retracted towards the drum inside, and a workposition in which they are radially extended and project from the drumin order to urge said work portion of the air bag against the radiallyinternal surface of a bead core being worked and coaxially arranged onthe drum surface;

fluid feeding means communicating with the inside of the air bag inorder to bring it from a deflated condition in which it is disposedsubstantially flattened in a cylindrical configuration against said drumto an inflated condition in which it is radially expanded so as to formfirst and second lobes located on axially opposite sides relative tosaid plurality of sectors urged against said bead core;

one annular opposition bell to be coaxially positioned around the airbag to counteract by an inner surface thereof, the radial expansion ofsaid first lobe, said first annular bell being axially movable relativeto the drum for enfolding the first lobe around one side surface and theradially external surface of the bead core;

a second annular opposition bell disposed coaxially opposite to saidfirst bell and designed to be positioned around the air bag in order tocounteract, by its inner surface, the radial expansion of said secondlobe, said second bell being axially movable relative to the drum,independently of said first bell, for enfolding the second lobe around asecond side surface and the radially external surface of the bead core.

Advantageously, said inflatable air bag is formed of a rubberized fabricmade inextensible in the axial direction relative to the air bag itself.

Said air bag, at the opposite ends of the work portion exhibitspremoulded centering pieces folded back through 360°.

In a preferred embodiment the apparatus further comprises at least oneelastic ring engaged circumferentially about said clasping sectors, saidelastic ring exhibiting at a radially external position, an engagementseat substantially mating the radially internal surface of the bead corebeing worked.

Said annular bells may also have differentiated diameters with respectto each other.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become more apparent from thedetailed description of a preferred embodiment of a method and apparatusfor looping up a coating structure on a bead core in vehicle tiresaccording to the present invention, which description is givenhereinafter by way of non-limiting example with reference to theaccompanying drawings, in which:

FIG. 1 is a diagrammatic part sectional view of an apparatus accordingto the invention, during the step of disposing a bead core around asupport drum;

FIG. 2 shows a working step subsequent to the one shown in FIG. 1,involving the engagement of the bead core by clasping sectors radiallymovable relative to the drum;

FIG. 3 shows a subsequent inflating step of an expansible air bagassociated with the drum within a pair of coaxial annular oppositionbells;

FIG. 4 shows a step in which one annular opposition bell is axiallymoved for enfolding one lobe of the inflatable air bag about the beadcore;

FIG. 5 shows a step subsequent to the one shown in FIG. 4, in which asecond annular opposition bell is axially moved towards the firstannular opposition bell;

FIG. 6 shows a step in which the two opposite flaps are overlapped oncompletion of the application of the coating structure to the bead core;

FIGS. 7 and 8 show two alternative operations (a looping operationwithout overlapping of the flaps and the application of a reinforcingelement, respectively) on a different type of annular reinforcingelement, also feasible with the machine of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, numeral 1 generally denotes an apparatus forlooping up a coating structure on a bead core in vehicle tires inaccordance with the present invention.

The apparatus 1 is arranged to apply a coating structure 3 to a beadcore 2 in vehicle tires. In the embodiment shown said coating structure3 essentially comprises at least one coating layer (skim coat) 4 made ofraw elastomeric material to which a ribbon 5 of rubberized fabric ispreferably coupled, in an overlaid relationship, which ribbon iscomprised of reinforcing cords conveniently made of a heat-shrinkablematerial such as nylon, for example.

For simplicity and clarity purposes, only in FIG. 1 the layer 4 andribbon 5 have been differently shown (using different sectionhatchings). During subsequent discussion in the present description suchlayer and ribbon will be generally referred to as strips.

The apparatus 1 comprises a support drum 6 rotatably supported incantilevered fashion on a horizontal axis and around which an inflatableair bag generally identified by 7, externally extends. In greaterdetail, the air bag has two circumferential beads 8 coaxial with saiddrum and sealingly engaged between the main body 9 and respectivecollar-shaped extensions 10 of the drum 6. Extending axially outwardlyfrom the beads 8 are two connecting portions 11 between the oppositeends of which a work portion 12 extends, at a radially externalposition.

Advantageously, the inflatable air bag 7 is made of a rubberized fabricprovided with reinforcing cords extending axially from one bead to theother, said cords making the air bag inextensible in an axial direction,that is along its extension in the plane of a radial cross section; atits ends where the connecting portions 11 are fastened to the workportion 12, the air bag has two premoulded folded back pieces slightlyprojecting from the drum 6 and acting as centering elements for the airbag on the drum itself, as clarified below.

In addition, the radially external surface of said work portion 12 iscoated with a layer of a material which is non-adhesive to a greatdegree for the purpose of minimizing adhesion between said surface andthe coating structure 3 which is fitted on said air bag for subsequentplacement on a bead core: for the purpose the silicone rubbers are agood option.

Also associated with the drum 6 is a plurality of clasping sectors 14(only one of which is shown in the accompanying drawings) which arecircumferentially distributed and slidably mounted for movement, in aradial direction, within the central body 9. The clasping sectors 14 areradially movable, upon command of a known actuator means (not shown),between a rest position in which, as shown in FIG. 1, they are radiallyretracted inwardly in the drum 6, and a work position in which, as shownin FIGS. 2 to 6, they are radially extended and project outwardly fromthe drum for retaining the bead core 2 being worked by exerting a thrustaction against the radially internal surface 2a of the bead core,through the work portion 12 of the air bag 7.

Preferentially, the clasping sectors 14 are interconnected by at leastan elastic ring 15 circumferentially engaged to said sectors and having,at a radially external position, an engagement seat 15a, the shape ofwhich substantially mates with that of the radially internal surface 2aof the bead core 2, through which said clasping action of the sectors onthe bead core is exerted.

Also provided is fluid feeding means 16 communicating with the inside ofthe air bag 7 in order to bring it from a deflated condition in which,as shown in FIG. 1, it is disposed substantially flattened in acylindrical configuration against the drum 6, to an inflated conditionin which, as shown in FIGS. 3 to 6, it is radially expanded therebyforming a first lobe 17 and a second lobe 18, disposed laterally onopposite sides with respect to said plurality of clasping sectors 14exerting pressure against said bead core. In the example shown, saidfluid feeding means are air passages 16 formed in the central body 9 ofthe drum 6 and opening into the air bag 7, in which passages compressedair or other working fluids under pressure are fed, in known andconventional manner.

In a simplified construction and operation of the machine and process ofthe invention, the lobes 17, 18 can be constantly put into fluidcommunication with each other, through the spaces existing between eachclasping sector 14 and a circumferentially adjoining sector.

This expedient ensures a pressure evenness in both lobes in a verysimple manner, when this feature is desired or is at all eventsacceptable.

Obviously, it may also be convenient, for the purpose of increasingflexibility, to modify the machine such that the lobes should be fedseparately from each other, in order to be able to use a differentpressure for each lobe.

The radial expansion of the lobes 17 and 18 is conveniently controlledby two corresponding annular opposition bells 19 and 20 to be coaxiallypositioned about the air bag 7 and movable, independently of each other,in an axial direction to the drum 6.

Preferentially, the first and second bells 19, 20 have differentiateddiameters with respect to each other, so that one of them, the firstbell 19 in this example, may be introduced telescopically into the otherwithout mechanical interference.

It is to be noted that the longitudinally inextensible character of theair bag 7 offers the possibility of controlling the expansion profile ofthe lobes 17 and 18 in an axial direction too, by varying the axialposition of each annular bell relative to the center line of the drum atthe beginning of the expansion step of the two lobes. In other words,since the air bag seen in radial cross section is transverselyinextensible and, when inflated, each lobe has one end held fast betweenthe adjacent edge of the bead core and the mating ring 15, it is clearthat the width of the lobe portion facing the bead core, that is theradial extension of the air bag portion freely expansible between thebead core edge and the axially inner edge of the bell depends both onthe diameter and the axial position of the bell on the drum when the airbag is being inflated.

In accordance with a looping method of the present invention, operationof the apparatus 1, described above mainly as regards structure, is asfollows.

The apparatus 1 is previously arranged with the air bag 7 in a deflatedcondition, as shown in FIG. 1. Under this situation, the circumferentiallaying down of the coating structure 3 around a median area of theinflatable air bag 7 is carried out with the aid of feed means not shownas known per se and not of importance to the ends of the invention. Thisstep can be executed in successive deposition stages during which saidribbon of rubberized fabric 5 and the elastomeric coating layer 4 arelaid down and superposed on each other.

Alternatively, laying down of the rubberized fabric ribbon 5 and coatinglayer 4 can take place simultaneously, for example by tangentiallyfeeding the strips at different points of the circumferential extensionof the drum 6 while the latter is being driven in rotation, or byfeeding the drum with the two strips previously coupled to each other.

In any case, the coating structure has an overall width larger than thecircumference of the cross sectional profile of the bead core 2, inorder to enable a mutual overlapping of its side edges following theenfolding operation around said bead core: said coating structure isfitted on said air bag at the clasping sectors 14 of the drum 6, at anaxially offset position relative to the equatorial plane of said drum,depending on the position that said overlapping must have relative tothe equatorial plane of the bead core.

Subsequently, by positioning means also not shown and known per se andnot of importance to the ends of the invention, the bead core 2 beingworked is placed in a coaxial relationship with the drum 6, radiallyoutward of the clasping sectors 14, on the center line of the equatorialplane of said drum.

The clasping sectors 14 are then expanded (FIG. 2) and urged against theradially internal surface 2a of the bead core 2, by simultaneouslymoving them from the rest position to the work position. Followingoperation of the clasping sectors 14, the mutual positioning of the beadcore 2 and coating structure 3 on the work portion 12 of the air bag 7is fixed.

By supplying air or other working fluid through the passages 16, the airbag 7 is then inflated (FIG. 3) in order to form the above describedfirst and second lobes 17, 18. The annular opposition bells 19, 20arranged coaxially at predetermined axial positions, and disposedlaterally on the other side from the bead core 2, counteract the radialexpansion of said lobes, which brings about expansion of the air bagalso in the axial direction. On the other hand, as already said, becausethe rubberized fabric forming the air bag 7 is axially inextensible,simultaneously with the radial expansion of the lobes 17, 18 and theexact positioning of the bells in relation to the equatorial plane ofthe drum, the control of the expansion profile of the lobes on theportion disposed alongside the bead core is also carried out, that is,the shape of the radially extending profile of each lobe is alsodetermined. The inner pressure of the air bag 7 can be advantageouslyadjusted to any desired value, without variations in volume of the airbag itself and/or other deformations thereof being involved.

In a preferential solution, the inner pressure of the air bag 7 at theend of the inflating step has a value in the range of 2 to 4 bars,preferably about 3 bars.

Under this situation, by effect of the inner pressure of the air bag 7,the first and second lobes 17, 18, upon the action of the work portion12, respectively cause bending of first and second side flaps 3b, 3c ofthe coating structure 3 towards a first and a second side surface 2b, 2cof the bead core 2; obviously, depending on the positioning of thecoating structure with respect to the bead core, said side flaps willhave different lengths.

Then the first opposition bell 19 is axially displaced (to the right asshown by the arrow) towards the bead core 2, so that the first lobe 17defined by the air bag 7 encompasses the bead core itself, as shown inFIG. 4. Under this situation, the first side flap 3b of the coatingstructure 3 is applied to the first side surface 2b and a portion of theradially external surface 2d of the bead core 2, with a thrust pressurecorresponding to the inner pressure of the air bag 7.

When the axial displacement of the first bell 19 has been completed, thesecond bell 20 is axially displaced (to the left, see arrow) towards thebead core 2, so that the second lobe 18 encompasses the bead core itselfin the same manner as with reference to the first lobe 17. Thissituation as shown in FIG. 5 causes the application of the second sideflap 3c to the second side surface 2c and the portion of radiallyexternal surface 2d of the bead core 2 not covered by operation of thefirst lobe.

It should be noted that, by virtue of the value of said thrust pressureduring the encompassing operation, the complete evacuation of airbetween the bead core surface and coating structure is achieved, as wellas a tensioned application of the reinforcing elements of saidstructure, that is the reinforcing cords of the ribbon 5.

In accordance with the present invention, the axial displacement of thesecond bell 20 goes on until the second lobe 18 comes into contact or inclose proximity with the first lobe 17 still urged against the firstside flap 3b of the coating structure 3 as shown in FIG. 5. Since thecoating structure 3 has an overall width slightly larger than thecircumference of the cross sectional profile of the bead core 2, at theend of this step the end edge 21 of the second flap 3c is still presenton the surface of the second lobe 18 separated from the bead core. Theedge 21, is to be overlapped with the end edge 22 of the first flap 3b,but this overlapping is inhibited by the presence of lobe 17.

During said movement of the second annular bell towards the bead core,the first annular bell can be moved away from the bead core, providedthat the first lobe 17 does not leave the end edge 22 of the first flap3b, but preferably it still keeps the achieved position and, ifnecessary, telescopically slides within the second bell 20 moving closeto the bead core itself. When the two lobes 17 and 18 have come intomutual contact, in the above described terms, in order that the end edge21 of the second flap 3c may be overlapped with that of the first flap3b, it is necessary for the first opposition bell 19 to be retractedaxially away from the bead core 2, so that the first flap will bedisengaged from the first lobe 17 and become accessible to the secondflap; consequently, the two bells 19 and 20 are moved together to theleft in an extension of the preceding translation of the second bell, sothat, while the first lobe 17 is progressively leaving the end edge 22of the first flap 3b, the second lobe 18 simultaneously causes the endedge 21 of the second flap 3c to be overlapped therewith and pressesthem on each other. These movements are indicated by the arrows in FIG.6. It should be noted that the first lobe 17 can disengage itself fromthe first flap 3b by the effect of the already mentioned very lowsurface adhesiveness of the air bag 7, so that the adhesiveness betweenthe metal bead core wires and the elastomer material layer, though weak,is however higher than that between the air bag 7 and coating structure3. In addition, the simultaneous combined translation of the two bellsreleases the flap 3b along reduced successive axial portions of itscircumferential extension on the bead core; thus it is possible toeliminate the risk that, as a result of the complete disengagement ofthe first lobe 17, the first flap 3b can be, by effect of the elasticreturn induced by the tensioned state in which the reinforcing elements(cords) are, separated from the radially external surface 2d of the beadcore 2 at one or more points of its extension, before overlapping hasoccurred and consequently before the second flap 3c has been joined byeffect of the intrinsic adhesiveness of the elastomeric material of thecoating structure itself. In fact, detachment of the first flap 3b wouldirreparably impair the correct execution of the enfolding or loopingoperation of the coating structure 3, which will make the whole beadcore 3 unusable.

Anchoring of the two end edges 21, 22 in mutual overlapping, aspreviously stated, is the condition ensuring the complete stability ofthe coating structure 3 applied to the bead core 2 during the necessaryhandlings for manufacturing the tire.

The axial combined translation of the two bells to the left as seen inFIG. 6 goes on therefore until the second lobe 18 has completely causedthe overlapping of the second flap 3c on the first flap 3b, the junctionbetween the two flaps being completed and the bead core has beencompletely incorporated in its coating structure. At this point, theclasping sectors 14 are radially contracted so that they release thelooped bead core from the mating ring 15 and the air bag 7 is deflatedand brought back to the starting configuration as shown in FIG. 1. Itwill be recognized that during this step, by virtue of the presence ofsaid premoulded pieces 13 acting as centering elements, the air bag canlay down again on the drum at a perfectly centered position relative tothe equatorial plane thereof; it therefore eliminates the risk that, anirregular deposition will take place in a subsequent expansion step whena second bead core is being worked. Thus the air bag will not create twoirregular lobes which would undesirably influence their expandingprofile and probably give rise to a faulty and useless enfolding of saidbead core.

In conclusion, it will be now recognized that the overlap width betweenthe two flaps depends on the difference between the width of the coatingstructure and the circumference of the bead core, whereas the overlapposition on the bead core surface depends on the mutual positioningbetween the center line planes of the bead core and its coating.

The present invention attains the intended purposes.

The present method and apparatus enable the application of the coatingstructure 3 by looping to be carried out in a very quick and reliablemanner even when the adhesion of the coating structure to the bead coresurfaces is very critical. With reference to the above describedembodiment, the application of the coating structure 3 to the outersurfaces of the bead core 2 is made particularly difficult due both tothe fact that the bead core, being made of bare metal, offers a lowadhesiveness, as known, to the elastomeric material and to the fact thatthe coating 3, because of the presence of the reinforcing cords in thestrip 5, exhibits a strong tendency to resume its original configurationafter the enfolding steps around the bead core section.

However, due to the important pressures exerted by the air bag 7 againstthe bead core surfaces and the reduced surface portion of the first flap3b that is disengaged from the corresponding lobe of the air bag beforethe second flap 3c is applied, all risks of even partial detachment ofsaid first flap from the bead core are avoided.

It will be also recognized that the method and apparatus in questionadvantageously carry out the application of the coating structure byexerting on said coating structure itself and the bead core, pressuresthat are uniformly distributed over the whole circumferential extensionof the bead core, unlike the known methods and apparatus, for examplethose carrying out looping by rolling, where bending of the coatingstructure and application of same to the bead core surfaces involve theinstantaneous application of pressures concentrated on distinct pointsof the circumferential extension of the bead core, thereby causinglocalized deformations and dangerous variations in the geometry of thetransverse section thereof.

In addition, the machine of the invention is also very versatile andcapable of putting into practice a series of working processes thataccording to the known art have hitherto required the use of severaldifferent machines. In particular, it is pointed out that the use of themachine of the invention is not limited to looping or enfolding of thepreviously described bead cores of the pack type, but is adapted toenfolding or partial coating of any type of bead core: FIGS. 7 and 8show, by way of example, two alternative operations (enfolding withoutoverlap of the flaps and application of a side reinforcing element) thatcan also be carried out by the machine of the invention, on current beadcores provided with known elastomeric fillers which have, in crosssection, a tapered shape, and are positioned on the radial outer surfaceof the bead core. It should be noted that these bead cores could also beof the above mentioned pack type, first enfolded according to theinvention and then assembled to said filler.

FIG. 7 shows looping of a well known annular reinforcing structure(comprising a bead core 30 assembled to a triangular shaped filler 31)with a strip 32 of elastomeric material or rubberized fabric havingflaps with identical (not shown) or differing radial extensions. On thecontrary, FIG. 8 shows a different operation comprising applying areinforcing strip 35 to a single axial surface of the bead core 33and/or the filler 34 thereof, which reinforcing strip may optionallyproject radially towards the outside from the filler top, withoutcausing deformations to the filler or, alternatively, by imposing anexactly controlled deformation to the filler through an appropriatecontrol of the axial strokes of the annular bells and/or the differentpressure values in the two lobes. Said controlled deformation may be,for example, the well known bending in an axial direction (not shown)that the bead core fillers must have when assembled to the carcass pliesby the use of drums of the rigid type, provided with an undercut on theshoulders.

From the foregoing description it will be apparent without furtherdetails being added that it is possible to execute the above operationsthrough application of the process of the invention with appropriatemodifications. For example, the combined translation of the two bells,as shown in FIG. 7, can be eliminated or both lobes may be used but witha single bell. It is clear that all these operations are possible due tothe combined effect of the independent movement of the two annularopposition bells together with the control of the expansion profile ofthe two lobes 17 and 18 under an inflating situation.

Obviously, the invention as conceived is susceptible of manymodifications and variations, all of them falling within the scope ofthe appended claims.

I claim:
 1. A method for looping and overlapping a coating structure ona motor-vehicle tire tread bead core, said core being formed of aplurality of metal wire coils, comprising the steps of:circumferentiallylaying down an elongated ribbon of a coating structure, comprising atleast one raw elastomeric material layer, on a median region of aninflatable air bag which is flattened against an outer cylindricalsurface of a support drum, said air bag having two circumferential beadscoaxial with said drum and sealingly engaged thereto; placing a beadcore in a coaxial position around said drum and radially outward of saidcoating structure, said coating structure having an overall widthslightly greater than the circumference of the bead core profile; movingradially outwardly a plurality of clasping sectors which arecircumferentially distributed on said support drum so as to pressagainst the radially inner surface of the bead core, in order to fix theposition of the bead core and coating structure on the inflatable airbag; inflating said air bag to cause a radial expansion thereof andforming first and second cooperating lobes in said air bag, one lobe oneach side of said bead core in order to laterally bend, on oppositeaxial sides of bead core, a first and a second side flap of the coatingstrip towards a first and a second side surface of said bead core;counteracting the radial expansion of said lobes by a first and secondannular opposition bell each of said bells being disposed in coaxialrelation around one of said lobes, one of said opposition bells having agreater diameter than the other opposition bell; axially moving thefirst annular opposition bell towards said bead core while in contactwith the first lobe for progressively applying the first side flap ofthe coating structure to a corresponding side surface and a portion ofthe radially outer surface of the bead core; axially moving the secondannular opposition bell towards said bead core while in contact with thesecond lobe for progressively applying the second side flap of thecoating structure to a corresponding side surface and to the radiallyexternal surface portion of the bead core which was not coated by saidfirst side flap; axially drawing the first annular bell away from thebead core, while maintaining the axial displacement of the secondopposition bell, for disengaging said first lobe from the first sideflap of the coating structure immediately before an end edge of saidsecond side flap is applied to the radially outer surface of the beadcore coated with said first flap, so that said first and second sideflaps are mutually fastened along respective end edges and overlappingeach other at the radially outer surface of the bead core.
 2. A methodaccording to claim 1 in which the circumferential laying down of saidcoating structure comprises the steps of:circumferentially depositing atleast one ribbon of rubberized fabric reinforced with heat-shrinkablematerial cords on said inflatable air bag; circumferentially depositinga coating layer of raw elastomeric material around said ribbon.
 3. Amethod according to claim 1 in which the inner volume of said air bag isstabilized to a predetermined and constant value by varying of theinflating pressure of the air bag.
 4. A method according to claim 1including controlling the axial expansion of the air bag together withcounteracting the radial expansion thereof during the bead coveringprocess.
 5. A method according to claim 4 in which said controlling ofthe axial expansion of the air bag is carried out by adjusting the shapeof the expansion profile of said lobes.
 6. A method according to claim 4in which said air bag is made of a rubberized fabric materialinextensible in the axial extension direction of the air bag.
 7. Amethod according to claim 1 in which said air bag is inflated to apressure ranging between 2 and 4 bars.
 8. A method according to claim 1including inflating said first and second lobes of the inflatable airbag to different fluid pressure values.